Model predicts loss of fish species

A global map predicting which reefs will lose species as a result of climate change has been published in Nature this week.

One of the greatest threats to the diversity of life on earth is climate change. Climate plays a substantial role in determining where a species occurs.

By building models scientists can predict how species will respond as their habitats shift. These models can direct the actions of conservationists towards species and areas that are most at risk.

You would be forgiven for assuming that species are most likely to be lost from areas where there will be high levels of warming. However, climate change driven patterns of extinction are unlikely to be that simple.

Most existing models have considered the fate of species across their entire distribution. While many species will see a reduction in their range size, species level extinctions will be relatively rare.

The study published in Nature this week investigates the probability of local species losses which will be much more common as temperatures change and species shift distributions. Rick Stuart-Smith from the University of Tasmania and his colleagues looked at the temperature ranges of almost 4000 reef animals including fish, sea slugs, octopuses and crabs to get a global picture of how marine communities may change across the planet.

For each location they considered how close local sea temperatures are to the edge of each species' maximum tolerable temperature. By combining these together they created a measure of how many species the local community is likely to lose with the currently predicted warming patterns.

"What this tool is doing is it's giving them a view of the likelihood of species being outside of their temperature ranges," explains Derek Tittensor from the World Conservation Monitoring Centre, whose news article was published alongside the study in Nature this week.

The map will be valuable to conservationists who are deciding on the location of marine reserves and protected areas. In particular, locations where summer sea surface temperatures are presently around 24 degrees Celsius are predicted to be most at risk of losing species as this is already the highest temperature that many species can tolerate.

Six (out of 75) marine regions, including the south-western Caribbean, were identified globally where it is predicted the sea temperature will rise above the temperature limit of more than 50% of local species by 2025.

It's not all bad news though. Marine communities in the western Mediterranean, despite being located in an area of high warming, are expected to be more resilient to climatic changes because many of the species survive elsewhere in warmer waters today.

"This measure of vulnerability that Stuart-Smith and colleagues have calculated is something that I think will be more broadly taken up by the scientific community," says Tittensor. "It will help to pinpoint those areas of high vulnerability where most species are going to have to adapt, or move, or perish..."

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